1. Technical Field
The invention disclosed broadly relates to semiconductor memory circuits and more particularly relates to improvements in radiation hardened, redundant circuits for memories.
2. Background Art
On semiconductor memory chips, spare memory locations are included to replace nonfunctioning regular locations. Reprogrammable redundant word and bit lines are designed into the chip to replace bad word or bit lines. This programming can be done at the time of manufacturing testing by blowing fuses included in the circuit, to deselect a bad word or bad bit line and to replace it with one of the redundant lines. The typical prior art redundancy selection circuit is selectively enabled by blowing a fuse contained in the redundancy circuit. One problem with such prior art circuits is that whether or not the circuit has been enabled, it still dissipates power during ordinary operation of the memory chip. The additional contribution of power dissipation is a disadvantage for such prior art designs. Other prior art redundancy selection circuits which are selected by blowing a fuse, include the feature that the redundancy circuit, after having been enabled by blowing a fuse, will be effectively enabled or disabled by the chip select signal applied to the memory chip. This provides for eliminating power dissipation contributed by the redundancy circuit when the memory chip is not selected. However this prior art redundancy circuit still suffers from additional power dissipation when the chip select signal is on regardless of whether the fuses have been blown or not. Once again, the minimization of power dissipation is a sought-after advantage which has been difficult to achieve in the prior art where redundancy circuits are used on memory chips. Still further, when a static memory chip is exposed to a high radiation environment, significant problems occur in maintaining the binary states of the storage cells. Prior art redundancy circuits have failed to provide for enhanced radiation hardness, because they typically include nodes having a floating potential.